Wiper system with extendible wiper arm

ABSTRACT

A wiper system, which is used especially for motor vehicles and in which the pendulum-motion of at least one wiper blade is overlapped by a motion of the wiper blade in its longitudinal direction. The wiper blade can be moved by means of a gearing that can be driven via a stroking shaft coaxially running to the wiper shaft. The stroking shaft is connected to a coupler via a stroking swivelling lever, which coupler is linked to an intermediate lever that can swivellably be driven around a fixed axis by the drive motor. In order to be able to wipe a big part of the windshield of a motor vehicle, the coupler passes a dead center when the intermediate lever is swivelling from the one reversing position to the other, in which dead center the coupler reverses the direction of its motion.

TECHNICAL FIELD

The present invention relates to a wiper system which is to be usedespecially for motor vehicles.

BACKGROUND ART

From practice as well as from a certain number of specifications, wipersystems for motor vehicles are known, in which during the operation ofthe pendulum-motion of the wiper arm and thus of the wiper blade carriedby the wiper arm a motion of the wiper blade is overlapped essentiallyin its longitudinal direction. This shift of the wiper blade is achievedby changing the effective length of the wiper arm. For this purpose thewiper arm can telescopically be constructed and can comprise a pistonwhich by means of a gear is shifted with respect to a guide housing thatmoves only in pendulum-motion. Such a construction is known, forinstance from the DE-PS 34 05 131, the EP-OS 0 218 192 or the EP-OS 0250 294. As to another construction, as it is shown in the DE-OS 34 05677, more or less only the link between the wiper blade and the wiperarm can be moved with respect to the wiper arm.

As to the wiper systems described in the specifications mentioned above,the motion for changing the effective length of the wiper arm via acoupler is derived form a rotary motion of a crank which isnon-rotatably seated on a stroking shaft coaxially running with respectto the wiper shaft.

From the DE-PS 34 05 131 and the EP-OS 0218 192, it is known to drivethe stroking shaft continuously in the same direction of rotation duringthe operation of the wiper shaft. Therefore, in one half of a wipingcycle it rotates in the same direction and in the other half of a wipingcycle it rotates in the opposite direction to the wiper shaft. Theconsequence thereof is that the wiping areas of the wiper blade whenbeing moved forward and backwards are different.

As to the wiper system of the DE-OS 34 05 677, the stroking shaft isdriven via a stroking swivelling lever in the opposite direction each tothe wiper shaft. For this purpose the stroking swivelling lever isconnected to an intermediate lever via a coupler, which intermediatelever has an axis of rotation fixed to the motor vehicle. A device rodis linked both to the intermediate lever and to a wiper shaft swivellinglever fastened to the wiper shaft, which wiper shaft swivelling lever isdriven by an electric motor via a crank drive. Due to the confrontationof the wiper shaft and of the stroking shaft, already small swivellingangles to the stroking crank seated on the stroking shaft lead to a bigchange of the angle between the stroking crank and the wiper arm andthus to a big change of length of the wiper arm.

It is known from the EP-OS O 250 294 to change the direction of rotationof the striking shaft within half a wiping cycle. Thus, the strokingshaft rotates both in the same and in the opposite direction to thewiper shaft within half a wiping cycle. The stroking shaft is driven viaa stroking swivelling lever being part of a crank drive, the other crankof which is connected with the stroking swivelling lever and is formedby a pinion meshing with a stationary toothed ring. Such a constructionis very expensive because of the pinion and of the toothed ring, for thepinion and the toothed ring are to mesh with each other with very littleplay in order to work quietly.

SUMMARY OF THE INVENTION

The object to the invention present is to develop a wiper system thatcan be adapted to different sizes of window panes at low coasts.

This object is achieved according to the invention by a wiper system inwhich, when the intermediate lever is swiveled from the one reversingposition to the other, the coupler passes a dead center in which thedirection of its longitudinal movement is reversed. Thus, the directionof rotation of the stroking shaft is not only reversed in the endpositions of the wiper arm, but also between the end positions of thewiper arm so that the stroking shaft during half a wiping cycle partlyrotates in the same and partly rotates in the opposite direction to thewiper shaft. For this purpose, no expensive pinion nor expensive toothedring are needed. In a wiper system according to the invention, differentrotary angles of the stroking shaft in the same and in the oppositedirection of rotation to the wiper shaft can easily be achieved bychanging the dead center of the coupler.

It is of a special advantage when the wiper blade is moved out of aparking position, the wiper shaft and the stroking shaft rotate in thesame direction at first. Therefore, the stroking shaft and the wipershaft can be arranged above a member of the wiper arm which cantangentially be extended to the two shafts, so that the gear which canbe driven by the stroking shaft as well as perhaps a housing receivingthis gear, at least in the parking position of the wiper arm, may besituated to a large extend underneath the lower edge of the pane to bewiped.

According to an aspect of the present invention the dead center of thecoupler can be achieved in an advantageous way be linking the coupler tothe intermediate lever at such a point that, when the intermediate leveris swivelling, the lever arm from the axis of the intermediate lever upto the linking point is made congruent with the longitudinal directionof the coupler.

Furthermore, it is of a special advantage when the effective lever armbetween the axis of the intermediate lever and of a drive rod drivingthe intermediate lever is smaller tan the effective lever arm betweenthe axis of the intermediate lever and the coupler. Thus, an especiallylong way of the coupler is achieved.

It may be useful to connect the coupler and the drive rod with theintermediate leer at a certain distance of each other in the directionof the axis of the intermediate lever. Therefore, the articulated axlesat the ends of the two rods can be arranged to a large extent inparallel direction to each other. Also a certain distance between thecoupler and the drive rod may be useful under the space conditions nextto the intermediate lever.

According to another aspect of the present invention the intermediatelever is advantageously arranged on the same side of the wiper shaft asthe drive motor. If there is another wiper shaft for driving anotherwiper arm, if driven by a stroking shaft or not, the intermediate leveris preferably arranged between the two wiper shaft. It is effective touse a support frame in which the wiper motor and/or several bearings forwiper shafts are fixed, also for fastening the intermediate lever. Apartfrom the wiper arms and wiper blades, the wiper system can then bemounted into the motor vehicle as a unit.

It is of an advantage that the intermediate lever can be driven via adrive rod by a wiper shaft swivelling lever non-rotatably connected witthe wiper shaft carrying the wiper arm with the wiper blade movable inits longitudinal direction. Thus, it is easily achieved that thereversing points of the wiper shaft swivelling lever and of theintermediate lever are temporally identical and that the wiping areasare the same when the wiper blade is moved forward and backwards.

An advantageous arrangement is obtained if a push rod, which can bemoved by the drive motor and is linked to the wiper shaft swivellinglever, and a drive rod are stituated on opposite sides of the wipershaft. It is also favorable, if the coupler and the drive rod, looked atin the direction of the wiper shaft, are axially displaced to each otheron opposite sides of the wiper shaft swivelling lever.

The intermediate lever can also directly be driven by a crank of thedrive motor via a drive rod.

The arrangement of the different elongated rods is simplified, if theintermediate lever and wiper shaft swivelling lever can be driven in thesame direction.

Several embodiments of a wiper system according to the invention areillustrated in the drawings. By means of the figures of these drawingsthe invention is described in detail in the following:

BRIEF DESCRIPTION O THE DRAWINGS

FIG. 1 is a view of a windshield of a motor vehicle with the parts of awiper system according to the invention visible from outside,

FIG. 2 illustrates the covered parts of a wiper system according to FIG.1 for driving a reciprocating stroking wiper arm and a conventionalwiper arm, the length of which is invariable,

FIG. 3 is a view of a wiper system according to FIG. 2 in the directionof Arrow F, whereby for clearness's sake unimportant parts are left out,

FIG. 4 an enlarged view of the crank gearing driven by the strokingshaft for changing the length of the wiper arm,

FIG. 5 is the schematic diagram of a second embodiment, which, however,is constructed without any cross linkages and

FIG. 6 is the schematic diagram of a third embodiment in which theintermediate lever is directly connected with the motor crank via adrive rod.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the windshield of a motor vehicle is designated by referencenumeral 10 on which windshield the wiping areas A and B of two wiperblades 12 ad 13 are indicated. The wiping area A is wiped by the wipingblade 13 which, as it is usually known, is only driven inpendulum-motion between two reversing positions. The wiping area B,however, is wiped by the wiper blade 12, which during thependulum-motion is moved also in its longitudinal direction. In thewiping area B, the size of a wiping area of a wiper blade driven only inpendulum-motion is indicated by dotted lines so that is can be seen thata bigger wiping area can be obtained by means of the wiper blade thatcan be moved to and fro. Thereby, the enlarged wiping area B on thedriver's side shall be produced. Both wiper blades 12 and 13 are linkedto a wiper arm 14 and 15, respectively. The longitudinal motion of thewiper blade 12 is achieved by changing the effective length of the wiperarm 134. The wiper arm 15 has a fixed length. The wiper arm 14 isnon-rotatably fixed onto a wiper shaft 16 and the wiper 15 isnon-rotatably fixed onto a wiper shaft 17. As shown in FIGS. 2 and 3,both wiper shafts 16 and 167 are rotatably located in wiper bearings 18and 19 fastened to a support frame 20 which is fixed to the motorvehicle. Thus, the wiper shafts 16 and 17 have axes fixed to the motorvehicle.

An electric motor 25 which comprises a worm-gear pair with a worm wheelas a driven wheel which is not illustrated any further, but is generallyknown, and which is screwed to the support frame 20 between the twowiper bearings 18 and 19 drives the two wiper shafts 16 and 17 via acoupler gearing. The coupler gearing comprises, first of all, therotating motor crank 26 which is non-rotatably fixed onto the drivenshaft 27. The one end of a first push rod 28 is linked to the motorcrank 26 via a ball pin 30 seated on the motor crank 26 and a ball joint31 injection-molded onto the push rod 28 and the other end of said pushrod 28 is linked to a swivelling lever 29 fixedly connected with thewiper shaft 16. The joint between the swivelling lever 29 and the pushrod 28 is also formed by a ball pi 30 on the swivelling lever and a balljoint on the push rod. The ball pin 30 passes through the swivellinglever 29 and comprises a ball on both sides of the swivelling lever. Bymeans of a second ball and of a ball joint 31, the one end of a secondpush rod 33 is linked to the swivelling lever 29. The other end of thepush rod 33 is also connected with a swivelling lever 34 via a ball pin30 and a ball joint 31, which swivelling lever is seated on the wipershaft 17 and protected against twisting with respect to the wiper shaft17.

During operation, the swivelling lever 29 is put into a to-and-fro, i.e.into a pendulum-motion via the rotating motor crank 26 and the push rod28. This pendulum-motion is also transferred onto the swivelling lever34 via the push rod 33. Thereby the swivelling levers and the push rodsare arranged in such a way that the two swivelling leers 290 and 34 movein phase. Thus the wiper arms 14 and 15 are both swiveled eitherclockwise or anti-clockwise.

By means of the gearing members described up to now, onlypendulum-motions of the wiper arms 14 and 15 can be produced. In orderto be able to change the length of the wiper arm 14 as shown in FIGS 1and 4, said wiper arm 14 consists more or less of a first section 490 inthe form of a guide housing carrying out only a pendulum-motion duringoperation and a second section 41 which, together with a piston 42, islocated in the guide housing 40 and can be shifted in longitudinaldirection, and to which the pendulum-motion is transferred from theguide housing 40. The stroking motion of the piston 42 is achieved by aswivelling stroking crank 43 connected to the piston 42 via a connectingrod 44 and the axis of which stroking crank 43 is identical with theaxis of the wiper shaft 16. Crank 43 and connecting rod 44 are also inthe guide housing 40. As it is made clear in the FIGS. 1 and 4, the axisof the wiper shaft 16 nd thus that the of the strike crank 43 is locatedbeside the axis of the piston 42. Thus, this piston 42 is not radially,but tangentially moved to the axis of the wiper shaft 16. Thearrangement is chosen in such a way that the piston 42 is underneath thewiper shaft 16 in the parking position of the wiper arm 14 illustratedin RIG. 1. Therefore the housing 40 asymmetrically located to the wipershaft 16 does not reduce the view through the windshield 10 in theparking position.

The stroking crank 43 fastened to a stroking shaft 45 leading throughthe hollow wiper shaft 16 and, looked at from the guide housing 40,projects the wiper shaft 16 beyond the bearing 18. At the projecting endof stroking swivelling lever 46 is fixed onto the stroking shaft 45,onto which stroking swivelling lever 46 the one end of a coupler 48 islinked via two cross linkages 47. At the other end the coupler 48 isarticulated to a lever 49 via a ball pin 30 and a ball joint 31.

This lever 49 is part of an intermediate lever 55 furthermore comprisinga swivelling lever 56 and a shaft 57 which can be rotated in a bearing58 and onto which at an axial distance on the one side of the bearingthe lever 49 and on the other side of the bearing the swivelling lever56 are fastened. By means of the axial displacement it is achieved thatthe plane of motion of the lever 49 and the cross linkages 47 betweencoupler 48 and the stroking swivelling lever 46 are identical to a largeextent. The bearing 58 is fixed onto the support frame 20 between thetwo wiper shafts 16 and 17 next to the motor 25.

The intermediate lever 55 can be moved via a drive rod 60, the one endof which is articulated to the swivelling lever 56 of the intermediatelever via two cross linkages 47 and the other end of which isarticulated to the wiper shaft swivelling lever 29 via a ball pin 30 anda ball joint 31. Thereby the linking point of the drive rod 60 at theswivelling lever 29 is with respect to the wiper shaft 16 opposite thelinking point of the push rod 28 on the swivelling lever 29. This meansthat the motions in longitudinal direction of the push rod 28 and of thedrive rod 60 are contrary to each other. Besides, the linking pointsbetween the push rod 28 and the swivelling lever 29 as well as betweenthe drive rod 60 nd the swivelling lever 29 are on different sides ofthe swivelling lever 29 and are axially displaced to each other. Thus,it is achieved that the drive rod 60 is moved to a large extent only inone plane.

During operation, the drive rod 60 is moved to and fro via the motorcrank 26, the push rod 28 ad the swivelling lever 29. This motion ischanged into a swivelling movement of the intermediate lever 55 via thecross linkages 47. Thereby, the arrangement is chosen in such a way thatthe intermediate lever 55 rotates in the same direction as theswivelling lever 29. During half a wiping cycle, i.e. during a motion ofthe swivelling lever 29 from the one reversing position to the other,the intermediate lever 55 is swiveled around approximately 140 degrees.The lever 49 being part of the intermediate lever 55 is also swiveledaround this angle. Swiveling the lever 49 is changed into a motion ofthe stroking swivelling lever 46 via the coupler 48 and the crosslinkages 47. The effective length of the leer between the drive rod 60and the intermediate lever 55 is smaller than the effective length ofthe lever between the coupler 48 and the intermediate lever 55 so thatthere is an increasing ratio of tho ways of the coupler 48 and of thedrive rod 60 in longitudinal direction. It is of importance that, uponswivelling of the intermediate lever 55 form the one end position to theother, the direction of the lever 49 and the longitudinal direction ofthe coupler 48 are made congruent. In the embodiment describedespecially, the lever 49 and the coupler 48 are then in a stretchedposition to each other. When passing the dead center, the coupler 48reverses the direction of its motion in longitudinal direction so thatthe direction of rotation of the stroking swivelling lever 46, too, isreversed without changing the directions of rotation of the intermediatelever 55. The reversal of the direction the stroking swivelling lever 46leads to a reversal of the direction of the stroking shaft 45, thestroking crank 43, the connecting rod 44 and of the piston 42.

In the FIGS. 1 to 3, different parts of the wiper system are shown inpositions occupied by them in the parking position of the wiper arms andwiper blades. When driving the swivelling lever 29 out of the parkingposition, that is clockwise in the view according to FIG. 2, theitermediate lever 55 is also swiveled clockwise. The lever 49, took ofthe intermediate lever 55 is swiveled clockwise. Thus the coupler 48, inthe view according to FIG. 2, is first moved to the left and thus thestroking swivelling lever 46 is also swiveled clockwise. When leavingthe parking position the wiper shaft 16 and the stroking shaft 45 movein the same direction at first. After a swivelling angle ofapproximately 90 degrees, the coupler 48 passes the dead center andreverses the direction of its longitudinal motion. Up to the reversingposition of the swievelling lever 29 and of the itermediate lever 55,the stroking swivelling lever 46 and the stroking shaft 45 then rotateanti-clockwise. When returning from the reversing position to theparking position, the stroking swivelling lever 46 and the strokingshaft 45 rotate clockwise until the dead center of the coupler 48 isreached. Afterwards they rotate anti-clockwise.

By varying the initial position of the lever 49, the size of the anglescan easily be changed, which angles are passed by the strokingswivelling lever 46 and the stroking shaft 45 in the same and in theopposite direction to the swivelling lever 29. In the embodiment shownin the FIGS. 1 to 4, the choice has been made an the lengths of thelevers and of the rods are adapted to each other in such a way that theangle around which the stroking shaft 45 rotates in opposite directionto the wiper shaft 16 is about 70 degrees and the angle around which thestroking shaft 45 rotates in the same direction as the wiper shaft 16,is about 170-180 degrees.

In the FIGS. 1 to 4, the position of the stroking crank 43 in the guidehousing 40 corresponding to the parking position is drawn in continuouslines. When leaving the parking position, the stroking crank 43 incorrespondence with the views according to the FIGS. 1 and 4 which arecontrary to the view according to FIG. 2, first rotates aroundapproximately 180 degrees anti-clockwise and thereby the piston 42 ismoved out of the guide housing 40 more and more. Then the coupler 48passes its dead center and the direction of rotation of the strokingcrank 43 is reversed. After that the stroking crank 43 passes an angleof approximately 70 degrees clockwise and thereby pulls the piston 42totally back into the guide housing 40.

As to the embodiment according to FIG. 5, which is only illustrated in aschematic diagram, a wiper shaft swivelling lever 29 is driven inpendulum-motion by an electric motor 25 via a motor crank 26 and a pushrod 28. The motion of the swivelling lever 29 is transferred to theintermediate lever 55 via a drive rod 60. The drive rod 60 is directlylinked onto the swivelling lever 56 of the lever 55 without any crosslinkages. The linking point of the drive rod 60 on the swivelling lever29 and the axis of the swivelling lever 29 and the linking point of thepush rod 28 on the swivelling lever 29 lie on one line. The coupler 48is directly linked onto the lever 49 of the intermediate lever 55 andonto the stroking swivelling lever 46 reach. The two levers 56 and 49 tothe intermediate lever 55 are arranged in an angle in such a way thatthe coupler 48 passes a dead center during the motion of the swivellinglever 56. In this dead center, the leer 49 and the coupler 48 are madecongruent. Contrary to the embodiment according to the FIGS. 1 and 4,however, lever 459 and coupler 48 are no stretched in the dead center,but are directed against each other about 180 degrees.

The positions of the gearing members shown in FIG. 5 are to correspondto the parking position of the wiper arms and wiper blades. Whenswitching on the electric motor 25, the swivelling lever 29 and theintermediate lever 55 are swiveled anti-clockwise. The lever 49 occupiessuch a position that the coupler 48 is first moved to the right so thatit swivels the stroking swivelling lever 56 clockwise, that is contraryto the direction of the swivelling lever 29. Having passed the deadcenter, the coupler 48 swivels the stroking lever 46 anti-clockwise.

The embodiment according to FIG. 6 only differs from that according toFIG. 5 in the fact that the intermediate lever 55 is directly driven bythe motor crank 26 of the electric motor 25 via a drive rod 60. Thereby,a shift of the phases between the swivelling motions of the swivellinglever 29 and of the intermediate lever 55 may occur, as it is shown inFIG. 6, for it can be seen that the push rod 28 and the motor crank 26in the illustrated parking position of the wiper arms and wiper bladesoccupy a stretched position, whereas the drive rod 60 and the motorcrank 26 enclose an angle not equal 180 degrees. This problem may besoled by separating the linking point of the drive rod 760 on the motorcrank 26 from the linking point of the push rod 28 so that the stretchedpositions are passed simultaneously. Another solution would be toarrange the intermediate lever 55 with respect to the motor 25 and theswivelling lever 29 in such a way that the drive rod 60 and push rod 28lie above each other in the stretched positions.

What is claimed is:
 1. A windshield wiper system comprising:a wiper armshaft; a drive means coupled to said wiper arm shaft for impartingreciprocating movement to said wiper arm shaft between first and secondreversing positions; a wiper arm having a first section by which saidwiper arm is mounted on said wiper arm shaft for pendulum-motion of saidwiper arm as said wiper arm shaft undergoes reciprocating movement and asecond section movable relative to said first section of said wiper armalong the longitudinal axis of said wiper arm; a wiper blade attached tosaid second section of said wiper arm; and mounting means for attachingsaid second section of said wiper arm to said first section of saidwiper arm for pendulum-motion of said wiper blade with said wiper armand movement of said wiper blade with said second section of said wiperarm along the longitudinal axis of said wiper arm during pendulum-motionof said wiper arm, said mounting means including:(a) a stroking shaftcoaxial with said wiper arm shaft and which moves in the same directionas movement of said wiper arm shaft from said first reversing positionto said second reversing position and moves in the opposite direction asmovement of said wiper arm shaft from said second reversing position tosaid first reversing position, (b) means connected between said secondsection of said wiper arm and said stroking shaft for imparting movementto said second section of said wiper arm along the longitudinal axis ofsaid wiper arm in response to movement of said stroking shaft, (c) astroking swivelling lever attached to said stroking shaft for pivotalmovement of said stroking shaft with said stroking swivelling lever, (d)a coupler connected at a first end to said stroking swivelling lever,(e) an intermediate lever mounted for swivellable movement between firstand second reversing positions and having a first end attached to asecond end of said coupler and a second end coupled to said drive means,said coupler passing through a dead center position while said immediatelever moves between said first and said second reversing positions ofsaid intermediate lever at which dead center position longitudinalmovement of said second section of said wiper arm is reversed.
 2. Awindshield wiper system according to claim 1 wherein movement of saidstroking shaft while said wiper arm shaft moves from said firstreversing position to said second reversing position is over a firstrotational angle which is greater than a second rotational angle ofmovement of said stroking shaft while said wiper arm shaft moves fromsaid second reversing position to said first reversing position.
 3. Awindshield wiper system according to claim 2 wherein said firstrotational angle is approximately 170 degrees to 180 degrees and saidsecond rotational angle is approximately 70 degrees.
 4. A windshieldwiper system comprising:a wiper arm shaft; drive means coupled to saidwiper arm shaft for imparting reciprocating movement to said wiper armshaft between first and second reversing positions; a wiper arm having afirst section by which said wiper arm is mounted on aid wiper arm shaftfor pendulum-motion of said wiper arm as said wiper arm shaft undergoesreciprocating movement and a second section movable relative to saidfirst section of said wiper arm along the longitudinal axis of saidwiper arm; a wiper blade attached to said second section of said wiperarm; and mounting means for attaching said second section of said wiperarm to said first section of said wiper arm for pendulum-motion of saidwiper blade with said wiper arm and movement of said wiper blade withsaid second section of said wiper arm along the longitudinal axis ofsaid wiper arm during pendulum-motion of said wiper arm, said mountingmeans including:(a) a stroking shaft coaxial with said wiper arm shaftand which moves in the same direction as said wiper arm shaft while saidsecond section of said wiper arm moves longitudinally outward from saidfirst section of said wiper arm, (b) means connected between said secondsection of said wiper arm and said stroking shaft for imparting movementto said second section of said wiper arm along the longitudinal axis ofsaid wiper arm in response to movement of said stroking shaft, (c) astroking swivelling leer attached to said stroking shaft for pivotalmovement of said stroking shaft with said stroking swivelling lever, (d)a coupler connected at a first end to said stroking swivelling lever,(e) an inebriate lever mounted for swivellable movement between firstand second reversing positions and having a first end attached to asecond end of said coupler and a second end coupled to said drive means,said coupler passing through a dead center position while saidintermediate lever moves between said first and said second reversingpositions of said intermediate lever at which dead center positionlongitudinal movement of said second section of said wiper arm isreversed.
 5. A windshield wiper system comprising:a wiper arm shaft; awiper arm having a first section by which said wiper arm is mounted onaid wiper arm shaft for pendulum-motion of said wiper arm as said wiperarm shaft undergoes reciprocating movement and a second section movablerelative to said first section of said wiper arm along the longitudinalaxis of said wiper arm; a wiper blade attached to said second section ofsaid wiper arm; mounting means or attaching said second section of sadwiper arm to said first section of said wiper arm for pendulum-motion ofsaid wiper blade with said wiper arm and movement of said wiper bladewith said second section of said wiper arm along the longitudinal axisof said wiper arm during pendulum-motion of said wiper arm, saidmounting means including:(a) a stroking shaft coaxial with said wiperarm shaft, (b) means connected between said second section of said wiper arm and said stroking shaft for imparting movement to said secondsection of said wiper arm along the longitudinal axis of said wiper armin response to movement of said stroking shaft, (c) a strokingswivelling leer attached to said stroking shaft for pivotal movement ofsaid stroking shaft with said stroking swivelling lever, (d) a couplerconnected at a first end to said stroking swivelling lever, (e) anintermediate lever mounted for swivellable movement between first andsecond reversing positions and having a first end attached to a secondend of said coupler and a portion between its swivel point and saidfirst end of said intermediate lever which is congruent with thelongitudinal axis of said coupler, and drive means coupled to a secondend of said intermediate lever and to said wiper arm shaft for impartingreciprocating movement to said wiper arm shaft between first and secondreversing positions and including;(a) a wiper arm shaft swivelling leverfixed to and pivotal with said wiper arm shaft, and (b) a drive rodconnected between said intermediate lever and said wiper arm shaftswivelling lever and spaced from said coupler along the axis of saidwiper arm shaft on an opposite side of said wiper arm shaft swivellinglever form said coupler, said coupler passing through a dead centerposition while said intermediate lever moves between said first and saidsecond reversing positions of said intermediate leer at which deadcenter position longitudinal movement of said second section of saidwiper arm is reversed.
 6. A windshield wiper system comprising:a wiperarm shaft; a wiper arm having a first section by which said wiper arm ismounted on said wiper arm shaft for pendulum-motion of said wiper arm assaid wiper arm shaft undergoes reciprocating movement and a secondsection movable relative to said first section of said wiper arm alongthe longitudinal axis of said wiper arm; a wiper blade attached to saidsecond section of aid wiper arm; mounting means or attaching said secondsection of said wiper arm to said first section of said wiper arm forpendulum-motion of said wiper blade with said wiper arm and movement ofsaid wiper blade with said second section of said wiper arm along thelongitudinal axis of said wiper arm during pendulum-motion of said wiperarm, said mounting means including:(a) a stroking shaft coaxial withsaid wiper arm shaft, (b) means connected between said second section ofsaid wiper arm and said stroking shaft for imparting movement to saidsecond section of said wiper arm along the longitudinal axis of saidwiper arm in response to movement of said stroking shaft, (c) a strokingswivelling lever attached to said stroking shaft for pivotal movement ofsaid stroking shaft with said stroking swivelling lever, (d) a couplerconnected at a first end to said stroking swivelling lever (e) anintermediate lever mounted for swivellable movement between first andsecond reversing positions, and having a first end attached to a secondend of said coupler and a portion between its swivel point and saidfirst end of said intermediate lever which is congruent with thelongitudinal axis of said coupler, and drive means coupled to a secondend of said intermediate lever and to aid wiper arm shaft for impartingreciprocating movement to said wiper arm shaft between first and secondreversing positions and including;(a) a wiper arm shaft swivelling leverfixed to and pivotal with said wiper arm shaft and mounted forswivellable movement in the same direction as said intermediate lever,and (b) a drive rod connected between said intermediate lever and saidwiper arm shaft swivelling lever said coupler passing through a deadcenter position while said intermediate lever moves between said firstand said second reversing positions of said intermediate lever at whichdead center position longitudinal movement of said second section ofsaid wiper arm is reversed.
 7. A windshield wiper system comprising:awiper arm shaft; a wiper arm having a first section by which said wiperarm is mounted on said wiper arm shaft for pendulum-motion of said wiperarm as said wiper arm shaft undergoes reciprocating movement nd a secondsection movable relative to said first section of said wiper arm alongthe longitudinal axis of said wiper arm; a wiper blade attached to saidsecond section of said wiper arm; mounting means for attaching saidsecond section of said wiper arm to said first section of said wiper armfor pendulum-motion of said wiper blade with said wiper arm and movementof said wiper blade with said second section of said wiper arm along thelongitudinal axis of said wiper arm during pendulum-motion of said wiperarm, said mounting means including:(a) a stroking shaft coaxial withsaid wiper arm shaft, (b) means connected between said second section ofsaid wiper and said stroking shaft for imparting movement to said secondsection of said wiper arm along the longitudinal axis of said wiper armin response to movement of aid stroking shaft, (c) a stroking swivellinglever attached to said stroking shaft for pivotal movement of saidstroking shaft with said stroking swivelling lever, (d) a couplerconnected at a first en to said stroking swivelling lever, (e) anintermediate lever mounted for swivellable movement between first andsecond reversing positions and having a first end attached to a secondend of said coupler and potion between its swivel point and said firstend of said id intermediate lever which is congruent with thelongitudinal axis of said coupler, and drive means, coupled to a secondend of said intermediate lever and to said wiper arm shaft for impactingreciprocating movement to said wiper arm shaft between first and secondreversing positions, said drive means including a drive motor, a crankat the output of said drive motor, a drive rod connected between saidcrank and said intermediate lever and a wiper arm shaft swivelling leverfixed to and pivotal with said wiper arm shaft and swivellable in thesame direction as said intermediate lever,said coupler passing through adead center position while said intermediate lever moves between saidfirst and said second reversing portions of said intermediate lever atwhich dead center position longitudinal movement of said second sectionof said wiper arm is reversed.